Hydrothermal Liquefaction Research Articles

Identification of Reaction Network Hypotheses for Complex Feedstocks from Spectroscopic Measurements with Minimal Human Intervention.

In this work, we detail an automated reaction network hypothesis generation protocol for processes involving complex feedstocks where information about the species and reactions involved is unknown. Our methodology is process agnostic and can be utilized in any reactive process with spectroscopic measurements that provide information on the evolution of the components in the mixture. We decompose the mixture spectra to obtain spectroscopic signatures of the individual components and use a 1-D convolutional neural network to automatically identify functional groups indicated by them. We employ atom-atom mapping to automatically recover reaction rules that are applied on candidate molecules identified from chemistry databases through fingerprint similarity. The method is tested on synthetic data and on spectroscopic measurements of lab-scale batch hydrothermal liquefaction (HTL) of biomass to determine the accuracy of prediction across datasets of varying complexities. Our methodology is able to identify reaction network hypotheses containing reaction networks close to the ground truth in the case of synthetic data, and we are also able to recover candidate molecules and reaction networks close to the ones reported in the previous literature studies for biomass pyrolysis.

Microwave-assisted two-stage catalytic hydrothermal liquefaction of Enteromorpha prolifera to produce furfural

To solve the increasingly energy shortage problem, the development of bioenergy from algal biomass has attracted much attention. Besides, algal blooms have caused serious environmental problems. The main purpose of this work is to produce furfural from hydrothermal liquefaction of Enteromorpha prolifera. The effects of reaction conditions (reaction temperature and reaction time) and catalyst types on furfural content are investigated. HZSM-5 catalysts modified with organic base TPAOH and composite catalysts loaded with Ni based on base modification are constructed. The results show that the highest furfural content of 45.4 %. The optimum reaction conditions are a reaction temperature of 180 °C, a reaction time of 30 min, and the catalyst selected is HZSM-5 modified with 1 mol/L TPAOH loaded with 5 wt% Ni. Response surface analysis is used to establish the relationship between furfural content and influencing factors. The results show that Ni loading is the most significant factor affecting furfural content.

Hydrothermal liquefaction of composite household waste to biocrude: the effect of liquefaction solvents on product yield and quality.

The hydrothermal liquefaction (HTL) of composite household waste (CHW) was investigated at different temperatures in the range of 240-360 °C, residence times in the range of 30-90 min, and co-solvent ratios of 2-8 ml/g, by utilising ethanol, glycerol, and produced aqueous phase as liquefaction solvents. Maximum biocrude yield of 46.19% was obtained at 340 °C and 75 min, with aqueous phase recirculation ratio (RR) of 5 ml/g. The chemical solvents such as glycerol and ethanol yielded a biocrude percentage of 45.18% and 42.16% at a ratio of 6 ml/g and 8 ml/g, respectively, for 340 °C and 75 min. The usage of co-solvents as hydrothermal medium increased the biocrude yield by 35.30% and decreased the formation of solid residue and gaseous products by 19.82% and 18.74% respectively. Also, the solid residue and biocrude obtained from co-solvent HTL possessed higher carbon and hydrogen content, thus having a H/C ratio and HHV that is 1.01 and 1.23 times higher than that of water as hydrothermal medium. Among the co-solvents, HTL with aqueous phase recirculation resulted in higher carbon and energy recovery percentages of 9.36% and 9.78% for solid residue and 52.09% and 56.75% for biocrude respectively. Further qualitatively, co-solvent HTL in the presence of obtained aqueous phase yielded 33.43% higher fraction of hydrocarbons than the pure water HTL and 7.70-17.01% higher hydrocarbons when compared with ethanol and glycerol HTL respectively. Nitrogen containing compounds, such as phenols and furfurals, for biocrudes obtained from all HTL processes, were found to be present in the range of 8.30-14.40%.

Climate change impacts of bioenergy technologies: A comparative consequential LCA of sustainable fuels production with CCUS

The use of sustainable biomass can be a cost-effective way of reducing the greenhouse gas emissions in the maritime and aviation sectors. Biomass, however, is a limited resource, and therefore, it is important to use the biomass where it creates the highest value, not only economically, but also in terms of GHG reductions. This study comprehensively evaluates the GHG reduction potential of utilising forestry residue in different bioenergy technologies using a consequential LCA approach. Unlike previous studies that assess GHG impacts per unit of fuel produced, this research takes a feedstock-centric approach which enables comparisons across systems that yield diverse products and by-products. Three technologies—combined heat and power plant with carbon capture, hydrothermal liquefaction, and gasification—are assessed, while considering both carbon capture and storage (CCS) or carbon capture and utilisation (CCU). Through scenario analysis, the study addresses uncertainty, and assumptions in the LCA modelling. It explores the impact of energy systems, fuel substitution efficiency, renewable energy expansion, and the up/down stream supply chain. All technology pathways showed a potential for net emissions savings when including avoided emissions from substitution of products, with results varying from −111 to −1742 kgCO2eq per tonne residue. When combining the bioenergy technologies with CCU the dependency on the energy system in which they are operated was a significantly higher compared to CCS. The breakpoint was found to be 44 kg CO2eq/kWh electricity meaning that the marginal electricity mix has to be below this point for CCU to obtain lower GHG emissions. Furthermore, it is evident that the environmental performance of CCU technologies is highly sensitive to how it will affect the ongoing expansion of renewable electricity capacity.

Algae Derived Carbon from Hydrothermal Liquefaction as Sustainable Carbon Electrode Material for Supercapacitor

With the worldwide awareness of sustainability, biomass-derived carbon electrode materials for supercapacitors have attracted growing attention. In this research, for the first time, we explored the feasibility of making use of the carbon byproduct from hydrothermal liquefaction (HTL) of microalgae, termed herein as algae-derived carbon (ADC), to prepare sustainable carbon electrode materials for high-performance supercapacitor development. Specifically, we investigated carbon activation with a variety of activating reagents as well as N- and Fe-doping of the obtained ADC with the intention to enhance its electrochemical performance. We characterized the structure of the activated and doped ADCs using scanning electron microscope (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and BET surface area and pore analysis, and correlated the ADCs’ structure with their electrochemical performance as evaluated using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), impedance, and cycle stability through an assembled symmetric two-electrode cell with 1 M H2SO4 as electrolyte. It was found that the ADC that is activated using KOH (KOH-ADC) showed the best electrochemical performance, and its specific capacitance was 14.1-fold larger with respect to that of the raw ADC and reached 234.5 F/g in the GCD test at a current density of 0.5 A/g. The KOH-ADC also demonstrated excellent capacitance retention (97% after 10,000 cycles at a high current density of 10 A/g) for stable long-term operations. This research pointed out a promising direction to develop sustainable electrode materials for supercapacitors from the carbon byproduct produced after HTL processing of algae.

Hydrothermal liquefaction of catering wastes towards biofuel intermediates

AbstractThe potential application of the hydrothermal liquefaction process on catering wastes, spent coffee grounds (SCG) and orange peels, towards reducing municipal wastes was examined in this study, targeting to the production of biofuel intermediates. The study was focused on the two main process parameters, temperature (280–350 °C) and residence time (5–60 min) while the other parameters such as biomass/solvent ratio and applied extractant were selected according to literature. The results indicated that spent coffee grounds are a more promising feedstock, rendering higher bio-crude oil yield than orange peels (34 wt% and 22 wt% respectively). The optimal conditions for each feedstock varied due to their different structural properties, which not only affected the products’ yields but also their quality. To better understand the distribution of the process degradation products and a part of the reaction’s pathway, the gas product was analyzed via GC-FID, and the aqueous phase was studied via HPLC analysis. Finally, the bio-crude oil was subjected to elemental, thermogravimetric, and GC-MS analysis to determine its quality and biofuel potential, based on which the bio-crude oil derived from spent coffee grounds showed promising results while orange peel–derived oil is of lower value. According to the study’s findings, the bio-crude oil can be utilized as a fuel substitute after being upgraded via hydrotreatment enabling the heteroatoms removal and enhancing its fuel properties. Graphical abstract

Hydrothermal liquefaction aqueous phase mycoremediation to increase inorganic nitrogen availability

Hydrothermal liquefaction aqueous phase (HTL-AP) is a waste product from a thermochemical process where wet biomass is converted into biocrude oil. This nutrient-rich wastewater may be repurposed to benefit society by assisting crop growth after adequate treatment to increase inorganic nitrogen, especially NO3−. This study aims to increase HTL-AP inorganic nitrogen, specifically NH3/NH4+ and NO3−, through fungal remediation for further use in hydroponic systems. Trametes versicolor, a white-rot fungus known for degrading a range of organic pollutants, was used to treat a diluted (5 %) HTL-AP for 9 days. No fungal growth was observed, but T. versicolor activity was suspected by laccase activity throughout cultivation time. NO3−-N and NH3/NH4+-N increased by 17 and 8 times after three days of fungal treatment, which was chosen as the appropriate time for HTL-AP fungal treatment as it resulted in the highest concentration of NO3−-N. The addition of nitrifying bacteria to the fungal treatment resulted in a twofold increase in NO3−-N concentration compared to the fungal treatment alone, indicating an enhancement in treatment efficacy. COD decreased by 51.33 % after 24 h, which may be related to the fungus’ capacity to reduce the concentration of organics in the wastewater; nonetheless, COD increased in the following days, which may be related to the release of fungal byproducts. T. versicolor shows promise as a potential candidate for increasing inorganic nitrogen in HTL-AP. However, future studies should primarily address HTL-AP toxicity, reducing NH3/NH4+-N while increasing NO3−-N, and hydroponics crop production after fungal treatment.

Multiphase Numerical CFD Simulation of the Hydrothermal Liquefaction Process (HTL) of Sewage Sludge in a Tubular Reactor

This article presents multiphase numerical computational fluid dynamics (CFD) for simulating hydrothermal liquefaction of sewage sludge in a continuous plug-flow reactor. The discrete particle method (DPM) was used to analyze the solid particles’ interaction in liquid–solid high shear flows to investigate coupling computational fluid dynamics (CFD). Increasing solid particles’ interactions were observed with the increasing liquid velocity. The study examined the influence of parameters such as flow rate, temperature, and residence time on the efficiency of bio-oil production. An increase in temperature from 500 to 800 K caused an increase in the amount of biocrude oil produced from 12.4 to 32.9% within 60 min. In turn, an increase in the flow rate of the suspension from 10 to 60 mL/min caused a decrease in the amount of biocrude oil produced from 38.9 to 12.9%. This study offers insights into optimizing the flow channel of tubular reactors to enhance the HTL conversion efficiency of sewage sludge into biocrude oil. A parametric study was performed to investigate the effect of the slurry flow rate, temperature, and the external heat transfer coefficient on the biocrude oil production performance. The simulation data will be used in the future to design and scale up a large-scale HTL reactor.

Comprehensive review of hydrothermal liquefaction data for use in machine‐learning models

AbstractHydrothermal liquefaction is a new, sustainable pathway to generate biogenic liquids from organic resources. The technology is compatible with a wide variety of resources such as lignocellulosic resources, organic waste, algae, and sewage sludge. The chemistry is complex and predictions of yields are notoriously difficult. Understanding and modeling of hydrothermal liquefaction is currently mostly based on a simplified biochemical analysis and product yield data. This paper presents a large dataset of 2439 experiments in batch reactors that were extracted from 171 publications in the scientific literature. The data include biochemical composition data such as fiber content and composition, proteins, lipids, carbohydrates, and ash. The experimental conditions are recorded for each experiment as well as the reported yields. The objective of this paper is to make a large database available to the scientific community. This database is analyzed with machine‐learning tools. The results show that there is no consensus on the analysis techniques, experimental procedures, and reported data. There are many inconsistencies across the literature that should be improved by the scientific community. Machine‐learning tools with a large dataset allow the generation of reliable yield production tools with a large application field. Given the accuracy of the data, the overall precision of prediction in an extrapolation to new results can be expected to be around 10%.

Wastewater-grown microalgae biomass as a source of sustainable aviation fuel: Life cycle assessment comparing hydrothermal routes

The present paper compared, through life cycle assessment (LCA), the production of aviation biofuel from two hydrothermal routes of microalgae cultivated in wastewater. Hydrothermal liquefaction (HTL) and gasification followed by Fischer-Tropsch synthesis (G + FT) were compared. Both routes included biomass production, hydrotreatment for biofuel upgrading, and product fractionation. Secondary data obtained from the literature were used for the cradle-to-gate LCA. G + FT had a higher impact than HTL in the 18 impact categories assessed, with human carcinogenic toxicity exerting the most harmful pressure on the environment. The catalysts were the inputs that caused the most adverse emissions. The solvent used for bio-oil separation also stood out in terms of impacts. In HTL, emissions for global warming were −51.6 g CO2 eq/MJ, while in G + FT, they were 250 g CO2 eq/MJ. At the Endpoint level, HTL resulted in benefits to human health and ecosystems, while G + FT caused environmental damage in these two categories, as well as in the resources category. In the improvement scenarios, besides considering solid, aqueous, and gaseous products as co-products rather than just as waste/emissions, a 20% reduction in catalyst consumption and 90% recovery were applied. Thus, in HTL, 39.47 kg CO2 eq was avoided, compared to 35.44 kg CO2 eq in the base scenario. In G + FT, emissions decreased from 147.55 kg CO2 eq to the capture of 8.60 kg CO2 eq.

Characteristics performance of adding coconut shell bio-oil to petroleum asphalt

Currently, there is considerable research on modified asphalt using bio-oil prepared by fast pyrolysis and hydrothermal liquefaction methods, but research on modified asphalt using bio-oil prepared by extraction method is scarce. In order to investigate the rationality and applicability of bio-oil produced by extraction method as a modifier added to petroleum asphalt, the coconut shell bio-oil modified asphalt was first prepared by blending the bio-oil at 2%, 3%, 4%, 5%, and 6% with petroleum asphalt. Their conventional performance was evaluated based on penetration, ductility, softening point and viscosity. Their rheological properties were obtained by dynamic shear rheometer, bending beam rheometer and multiple stress creep and recovery. The modification mechanism was analyzed by gel chromatography and Fourier transform infrared reflection. The results show that the bio-oil can significantly improve the low temperature performance and fatigue resistance of the asphalt, but it is not good for the high temperature performance and temperature-sensitive performance. The added bio-oil increases the content of light components and decreases the content of asphaltenes in the asphalt, and the modification of petroleum asphalt by the bio-oil is not only a physical mixing but also a chemical process. The bio-oil has good compatibility with the asphalt binder.

Enhancing Sewage Sludge Treatment with Hydrothermal Processing: A Case Study of Adana City

As a byproduct of municipal wastewater treatment systems, sewage sludge has traditionally been treated in low-value applications such as landfilling, posing significant environmental risks due to its pollutant content. However, there is a growing interest in utilizing the energy potential of sewage sludge through thermochemical conversion methods. Among these methods, hydrothermal liquefaction (HTL) has come to the fore as a promising green approach, offering an environmentally friendly means of extracting bio-oils and biochemicals from sewage sludge. In this study, the HTL method, regarded as an innovative approach among sewage sludge treatment methods apart from incineration, pyrolysis, and landfilling, is comparatively investigated in terms of greenhouse gas (GHG) emissions alongside other methods. In particular, this study analyzes the projected amount and various characteristics of sewage sludge that could potentially be generated by 2030 for the city of Adana, which currently produces approximately 185 tons of sewage sludge per day. The findings indicate that without intervention, sludge production is projected to reach 68,897 tons per year by 2030. Moreover, this research demonstrates that the utilization of HTL for sludge treatment results in a reduction of emissions by approximately 7-fold compared with incineration of sewage sludge.

THE IMPORTANCE OF BIOETHANOL AS AN ENVIRONMENTALLY CLEAN FUEL

This article is a review based on literature sources. The production technology and areas of application of bioethanol, as well as ways to intensify the production of alcohol obtained from these natural sources, are analyzed. One such method is biomass liquefaction. Modern technologies for converting biomass into valuable biofuels were studied. Common biomass liquefaction technologies are indirect liquefaction and direct liquefaction. Direct biomass liquefaction involves converting biomass into bio-oil, and the main technologies are hydrolytic fermentation and thermodynamic liquefaction. Based on thermodynamic liquefaction, it can be divided into fast pyrolysis and hydrothermal liquefaction. In addition, this review provides an overview of the physicochemical properties of biodiesel and common methods for its processing. Keywords: bioethanol, yeast, natural food waste, purchasing biofuel.

Sustainable biorefining: Hydrothermal liquefaction of diatom biomass for bio-crude and nano-biosilica recovery

Diatom, a unique species of microalgae is a highly promising resource for the production of valuable bio-crude and silica nanomaterial. However, the complex nature of diatom cell structure presents significant downstream processing challenges and leads to inefficient bio-product recovery. To overcome this challenge, this study aimed to develop a one-step approach for the valorization of Denticula sp. dominated diatom consortium using hydrothermal liquefaction (HTL) process with the recovery of three major products. The first output, referred to as biocrude, constituted 22% of the total yield, consisting of 9.5% unbound bio-crude and 12.5% cell wall-bound organic fraction. The bio-crude consisted primarily of oxidized and desirable organic compounds like alcohols (24.4%), long-chain saturated hydrocarbons (23.6%), and esters (17.6%), with only a few undesirable nitrogen-containing compounds (18.9%). The second resultant product comprised nanoporous bio-silica structures, yielding 56%. These silica structures exhibited enhanced quality in comparison to the conventional thermal extraction technique employed for their retrieval and were found to be three-dimensional, highly porous, intact silica structures with low trace elements and a high surface area (53.7 m2 g−1). The third acquired product, the aqueous fraction, was observed to possess elevated levels of nitrate-nitrogen (440 mg L−1) and total dissolved phosphate (975 mg L−1). Overall, the study highlights the potential of HTL as an efficient diatom downstream processing method that allows for the complete valorization of intermediates, resulting in a sustainable biomass conversion and product recovery technology.

Co-liquefaction of α-cellulose and phycocyanin: A preliminary study

Hydrothermal liquefaction (HTL) is an efficient technology for converting biomass to platform compounds. It has great potential for reducing the dependence on fossil fuels. The HTL of waste biomass has been extensively studied in recent years due to both its environmental and economic benefits. However, most woody waste contains a large amount of cellulose, and it is difficult to be sufficiently decomposed to valuable chemicals. Phycocyanin, a key component of algae, is easily degraded under high-temperature liquefaction conditions. In this work, focusing on bio-oil generation properties, the co-liquefaction characteristics and synergistic mechanisms of α-cellulose and phycocyanin were explored. The findings revealed a maximum bio-oil yield of 33.1 wt% under the optimal conditions (300 °C for 40 min), with a notable positive synergistic effect of 13.5 wt%. Chemical composition analysis indicated distinct compositional differences between the bio-oils derived from individual and dual feedstock. The amounts of pyridine and pyrimidine compounds increased due to the enhanced co-liquefaction. The results also highlighted the influence of temperature on the degree of conversion and product distribution. Finally, preliminary chemical reaction pathway was elucidated, underscoring the potential of integrating microalgae and woody biomass for enhanced bio-oil production.

Evaluating hydrothermal liquefaction hydrochar from sewage sludge as a phosphorus resource through struvite production

Hydrothermal liquefaction (HTL) has attracted considerable attention for valorizing sewage sludge to biofuels while the solid residue, hydrochar, has received little attention for its final application. In the current work hydrochar recovered from hot separation in a pilot-scale HTL plant is evaluated for its nutrient value, in particular as a sustainable Phosphorus (P) resource. Following thorough characterization of the hydrochar, P recovery as struvite (NH4MgPO4·6H2O) is investigated to produce a fertilizer with a lower heavy metal content that could be used in current agricultural practices. P extraction using inorganic (hydrochloric and sulphuric) and organic (citric) acids is evaluated by applying 0.1–1 mol/L of acids for 1–12 h with a liquid/solid ratio of 10 mL/g. A second-order polynomial model was established by response surface methodology (RSM) to predict the P extraction with different acids. The optimum operating conditions for maximum P extraction (94 %) are suggested as 0.7 M of acid strength (H2SO4) and 6.5 h of extraction time. Addition of citric acid (CA) during the struvite precipitation from acid-leached P solution was found to improve the struvite purity from 36.6 % to 54 % with a reduction in heavy metal content. Furthermore, morphological analysis validated the formation of struvite. Upon comparison with the regulations, hydrochar was found to exceed some of the heavy metal limits but was low in polyaromatic hydrocarbons (PAHs), per- and polyfluorinated substances (PFAS) and showed low toxicity to Aliivibrio fischeri. P extraction and struvite precipitation are shown to reduce heavy metal contents below regulatory limits with P recoveries from 40 % to 67 %. Thus, as an alternative to direct land application of hydrochar, harvested struvite from hydrochar could be applied as a fertilizer with no apparent environmental risk.

Ultrafiltration fractionation of potentially inhibitory substances of hydrothermal liquefaction aqueous phase derived from municipal sludge

Hydrothermal liquefaction (HTL) is a promising thermo-chemical technology for municipal sludge treatment due to its potential for biocrude oil recovery and minimizing biosolids management costs. However, the process generates a high volume of an aqueous byproduct that needs to be treated due to its high chemical oxygen demand (COD) and various organic and inorganic compounds. Although the aqueous phase is known to contain recalcitrant and potentially inhibitory substances that may affect its biological treatment, their molecular weight distribution (MwD) and its impact on anaerobic biodegradability are poorly understood. Ultrafiltration (UF) was conducted to fractionate HTL aqueous into different molecular weight (Mw) fractions using 300, 100, 10, and 1 kDa membranes. Mesophilic biochemical methane potential (BMP) assays were conducted to assess the anaerobic biodegradability of each fraction, and the first-order model was used to calculate the degradation kinetics of potential inhibitory compounds. The highest percentage of organics (65 %) was found in the Mw<1 kDa range, whereas the 10>Mw>1 kDa had the lowest percentage (8 %). There was no significant difference in the cumulative specific methane produced from various Mw fractions (p>0.05). The Mw<1 kDa fraction had the highest first-order specific methane production rate (0.53 day−1), whereas the unfiltered HTL had the lowest (0.38 day−1). Although UF fractionation increased the rate of anaerobic degradation of HTL aqueous for the Mw<1 kDa fraction, the observed methane potential was only 55 % of the theoretical value. This implies that 45 % of COD remains undegraded even after permeation through the lowest Mw cut-off membrane. Therefore, further characterization of HTL aqueous is needed for compounds with molecular weights below 1 kDa to fully understand the nature of inhibitory organics and their impact on anaerobic digestion. Furthermore, pretreatments utilizing techniques such as adsorption and advanced oxidation may be necessary to enhance the specific methane yields from various HTL aqueous fractions, thereby bringing them closer to the theoretical yield.

Influence of catalysts on the hydrothermal liquefaction of municipal primary sludge: Upgrading to a higher quality biocrude

Effect of homogeneous and heterogeneous catalysts on hydrothermal liquefaction of primary sludge was studied. Biocrude, biochar, aqueous phase and biogas were all affected, in terms of quantity and quality. HTL without any catalyst attained a biocrude yield of 37.7 % (w/wVS). The best improvements in biocrude yield are observed with CuSO4 (10 %), 42.20 % (w/wVS) and TiO2 (20 %), 41.90 % (w/wVS). All experiments with catalyst produced a biocrude with HHV higher than 30 MJ/kg and with carbon content higher than 60 %. The analysis demonstrated that the major fraction of biocrude were asphaltenes, the heavier phase. While, the light phase, oils, in most of the cases, contained more saturates than polars. Biochar and aqueous phase were recuperated with high organic contents, that enables their usages in further applications. Even though gas fractions were small, their compositions varied between CO, CO2 and hydrocarbons. Catalysts were normally recuperated with the solid phase, except some cases due to their particle sizes. Most of the ashes of primary sludge were transferred to biochar. Some parts of them went to the aqueous phase and biocrude during separation process.

A review on hydrothermal treatments for solid, liquid and gaseous fuel production from biomass

The rise in the population and rapid industrialization has resulted in a rise in the global energy consumption. In order to minimize the load on the conventional energy sources, various studies are being conducted for the production of biofuels by hydrothermal operations. Unlike conventional processes of biofuel production, wet biomass can be directly utilised without drying in turn reducing the energy consumption. Feedstocks such as agricultural residue, forest residue, energy crops, algae, sludge, litter and food waste can be utilised for the production of biofuels. The operation intensities (temperature and pressure) can be varied from pressurized hot water to supercritical water. Hydrothermal operations depending on the operating parameters are further subcategorised into four types namely wet torrefaction (WT), hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) and hydrothermal gasification (HTG). Even though the operating conditions of wet torrefaction and hydrothermal carbonization lie in similar categories, the difference is clearly visible in the level of carbonization. Due to the wide range of operating temperature and pressure, mainly three different products are produced through hydrothermal operations. The temperature range for wet torrefaction can be limited between 150 and 220 °C, whereas the HTC process can be between 200 and 260 °C. At higher temperatures (260 – 370 °C) in hydrothermal liquefaction (HTL), increased isomerization, depolymerization and repolymerization of organic compounds within the biomass occurred, causing liquid product (bio-oil) to be formed as the major product. Hydrothermal gasification can be further subcategorised into three types: namely aqueous phase refining, near critical water gasification and supercritical water gasification (SCWG). This paper has reviewed different hydrothermal operations based on biofuel production from different biomass.

Integrated e-Methanol and Drop-in Fuels Hydrothermal Liquefaction Platform-Techno-Economic and GHG Emissions Assessment for Grid-Connected Plants under Flexible BECCU(S) Operation.

This study examines the combined production of drop-in fuels and methanol using hydrothermal liquefaction (HTL) as a technological basis in the context of bioenergy and power-to-X (PtX) applications. Given the increasing need for flexibility in a system dominated by fluctuating renewable power, we evaluated flexible methanol operation as a strategy to harness global greenhouse gas (GHG) emissions in a grid-connected HTL setup. In this operation, the biogenic CO2 destination is alternated between methanol synthesis bioenergy with carbon capture and utilization and combined underground storage depending on the hourly electricity price and grid carbon intensity. The results indicate that the strategy has potential to maintain the average fuel carbon intensity within the 65% GHG reduction threshold set by the renewable energy directive III at a minimum methanol price of 870 EUR/t. This approach could facilitate implementation as it does not require dedicated renewable power generation and hydrogen storage, potentially decreasing costs compared to semi-islands and off-grid PtX systems.